Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$112.29	9.676%	$123.1552	$123.16	$123.15	$123.20
Purchase #2	$175.67	4.674%	$183.8808	$183.88	$183.90	$183.90
Purchase #3	$52.64	8.111%	$56.9096	$56.91	$56.90	$56.90
Purchase #4	$153.83	10.823%	$170.479	$170.48	$170.50	$170.50
Purchase #5	$28.54	12.672%	$32.1566	$32.16	$32.15	$32.20
Purchase #6	$134.38	5.211%	$141.3825	$141.38	$141.40	$141.40
Purchase #7	$209.92	9.734%	$230.3536	$230.35	$230.35	$230.40
7 purchase totals =	$867.27		$938.3173	$938.32	$938.35	$938.50